KA3: membrane proteins: movement of molecules across membranes Flashcards
describe the fluid mosaic model of the cell membrane
-describes the structure of the plasma membrane
-comprised of a bilayer of phospholipids molecules and a patchwork of protein molecules
-phospholipids are constantly changing position, giving the membrane its fluid quality
-cholesterol may be found within the membrane, acting to reduce membrane fluidity, it also prevents the membrane from solidifying at low temps
what do regions of hydrophobic R groups allow?
Strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer
describe the head region of the phospholipid bilayer
hydrophilic (attracted to water)
Describe the tail region of a phospholipid.
- made up of the fatty acids (uncharged and non-polar)
- hydrophobic (repelled by water)
some integral membrane proteins are…
transmembrane proteins
Describe integral proteins
-held firmly in place within the membrane
-interact extensively with the hydrophobic region of membrane phospholipids
describe peripheral proteins
-have hydrophilic R groups on their surface
-bound to the surface of membranes by ionic and hydrogen bond interactions
-interact with the surfaces of integral membrane proteins
What is the phospholipid bilayer?
a barrier to ions and most uncharged polar molecules
give examples of molecules which pass through the bilayer by simple diffusion
oxygen and carbon dioxide
Describe facilitated diffusion
the passive transport of substances across the membrane through specific transmembrane proteins.
how do cells perform specialised functions?
different cell types have different channel and transporter proteins.
what are most channel proteins in animal and plant cells?
highly selective
what are channels?
multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane
what can channel proteins be and what is this effect?
-gated
-change conformation to allow or prevent diffusion
how does water cross the membrane?
diffusion through the lipid bilayer and through water channels called aquaporins
what are ligand-gated channels controlled by?
binding of signal molecules
what are voltage-gated channels controlled by?
changes in ions concentrations
what is the role of a transporter protein?
bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane
why do transporters alternate between two conformations?
so that the binding site for a solute is sequentially exposed on one side of the bilayer, to the other
describe the process of active transport
-uses pump proteins that transfer substances across the membrane against their concentration gradient
what are pumps that mediate active transport?
transporter proteins coupled to an energy source
give an example of active transport
sodium potassium pump
what is required for active transport?
a source of metabolic energy
why do some active transport proteins hydrolyse ATP?
to provide the energy for the conformational change required to move substances across the membrane
describe the role of ATPases
hydrolyse ATP
